This invention relates generally to electro-optic projection displays such as liquid crystal projection displays.
It has been appreciated for some time that the addition of an luminosity channel to a projection display, including an electro-optic display, would be advantageous. The luminosity channel contains the lightness and darkness information and, viewed by itself, looks like a gray scale image. A substantial portion of the image detail exists in the luminosity channel. The luminosity channel uses white light while the conventional electro-optic display uses a set of three spatial light modulators for each of the primary color planes.
It is believed that luminosity channels have not been widely used heretofore, despite the understanding that the resolution of the projection display would be substantially enhanced. This may be because of the problem with light efficiency which arises from extracting a significant portion of the light for a four channel system. Thus, while those skilled in the art may appreciate the benefits of luminosity channel, it has not been widely adopted in practice.
One known approach to providing luminosity channel is utilized in the Texas Instruments digital mirror based projection engines. However, the luminosity channel is provided by field sequential addressing mode using a color wheel. The color wheel has slots for the primary color planes and two white light or luminosity channels. While time sequential approaches have some advantages, they also suffer from some problems. Firstly, their optical efficiency is low. Secondly, they suffer from color breakup. It is not believed that the addition of a luminosity channel in this fashion will sufficiently improve the overall characteristics of the display to make the addition of a luminosity channel cost effective.
Thus, there is a continuing need for a way to provide a luminosity channel without adversely effecting the characteristics of the overall display, including its light efficiency.